1. Field of the Invention
This invention relates to remote sensing and, more particularly, to active multispectral remote sensing.
2. Description of Related Art
Multispectral remote sensing may be conceptualized as viewing radiation reflected and/or emitted from a certain location in two or more wavelength regions. In other words, multispectral sensing measures the intensity of radiation for the location at two or more different wavelengths. Active multispectral remote sensing utilizes a source of radiation (e.g., infrared, visible, or ultraviolet light) to illuminate a target while measuring the reflected and/or emitted radiation.
One scheme for performing active multispectral remote sensing is to stare at the location with a single detector, while sequentially illuminating the location with two or more different wavelengths. Such a scheme may be unsuitable, however, for sensing from a remote platform that is moving relative to the location under measurement. To stare at the location for a long enough time may entail, for example, the use of a scanning/tracking mirror on the moving platform, which may introduce undesired errors or complexity.
Another scheme for performing active multispectral remote sensing is to stare at the location with multiple detectors, while simultaneously illuminating the location with two or more different wavelengths. Each detector is typically coupled to an optical filter, so that each of the detectors only detects one of the different wavelengths. Spectral features of interest, however, may necessitate narrowband optical filters whose passbands are closely spaced in wavelength. Such narrowband optical filters, however, may be expensive to implement, and may also cause undesired crosstalk between detectors.
Thus, there is a need in the art to perform active multispectral remote sensing from a moving platform in an inexpensive and precise manner.
Systems and processes consistent with the principles of the invention may include, among other things, a moving or stationary remote platform that may emit and detect different wavelengths of radiation toward a location at different times. A spectrum of that location may be assembled from data collected at the different times.
In accordance with one purpose of the invention as embodied and broadly described herein, an active system for obtaining a multispectral image of a target may include a number of sources configured to emit radiation toward different locations on the target. At least two of the number of sources may emit radiation of different wavelengths. A number of detectors may correspond to the number of sources and may be oriented toward the different locations on the target. At least two of the number of detectors may be configured to detect the radiation of different wavelengths. A processor may be configured to construct spectra of the different locations on the target from data obtained by the number of detectors as the system moves relative to the target.
In another implementation consistent with principles of the invention, a mobile remote sensing platform may include a first source having a first field of view and being configured to emit radiation of a first wavelength. A first detector may have a field of view that overlaps the first field of view and may be configured to detect the radiation of the first wavelength. A second source may have a second field of view that is separate from the first field of view and may be configured to emit radiation of a second wavelength. A second detector may have a field of view that overlaps the second field of view and may be configured to detect the radiation of the second wavelength.
In a further implementation consistent with principles of the invention, a method for constructing a spectrum may include emitting first and second wavelengths of radiation toward first and second locations, respectively. The first and second wavelengths of radiation respectively reflected from the first and second locations may be detected at a first time. The first and second wavelengths of radiation may be emitted toward the second location and a third location, respectively. The first and second wavelengths respectively reflected from the second and third locations may be detected at a second time. A spectrum for the second location may be constructed using the wavelengths of radiation detected at the first and second times.
In a yet another implementation consistent with principles of the invention, a method for obtaining a spectrum of a location by a moving platform may include emitting radiation of a first wavelength toward the location and detecting radiation of the first wavelength reflected from the location. The method may include moving the platform relative to the location. The method may also include emitting radiation of a second wavelength toward the location and detecting radiation of the second wavelength reflected from the location. The method may further include assembling a spectrum of the location using the detected radiation of the first and second wavelengths.
In a further implementation consistent with principles of the invention, a method for obtaining a spectrum of a location by a remote platform may include sequentially illuminating the location with different wavelengths of radiation by moving the platform. The different wavelengths of radiation reflected from the location may be sequentially detected and converted into data. A spectrum of the location may be assembled from the data that was sequentially collected.